They were flown into Hong Kong in substandard conditions, but today they're being sent home first class.

About 600 freshwater pig-nosed turtles - a protected species native to Australia and New Guinea - were smuggled into the city in January, barely surviving dehydration in badly packed containers.

Today, they are to be taken from their temporary shelter and flown to a new home in Indonesia, arranged with the help of animal rescue groups there. For the past nine months, the turtles have been cared for by officers at Kadoorie Farm and Botanic Garden. The animals have doubled in size to just over 10cm in length, gaining enough strength to face the challenge of adapting to their new home in a national park north of Merauke city in Papua province.

The 600 small turtles are the survivors from an original group of 785 seized in a routine inspection at the airport's cargo terminal, said Alfred Wong Kwong-chiu, an endangered species protection officer with the Agriculture, Fisheries and Conservation Department. The animals were found in an overcrowded, waterless one-cubic metre wooden box, a clear violation of international guidelines on wild animal transfer. Nearly 200 of them soon died due to poor health.

Wong said: 'Most of these turtles were probably hatched not long before they were stuffed into the cargo plane. Since they were so small, they probably weren't sent for human consumption; they were more likely sent as pets because they're cute.'

The turtles are listed in appendix two of the Convention on International Trade on Endangered Species, which applies to species that are not necessarily threatened with extinction but may become so unless their trade is strictly regulated. Their population has declined by an estimated 50 per cent in recent decades, due to poaching and habitat degradation. The agriculture department has investigated the trading company that owned the consignment, but there was insufficient evidence to bring charges, Wong said. Under Hong Kong law, illegal trade in wild animals carries a maximum fine of HK$500,000 and one year in jail.

Turtles ranked as the second most popular pets, after fish, in a 2005 poll conducted by the department, Wong said. But pig-nosed turtles are less popular than other turtles because they are more sensitive to temperature and water quality. Adults can grow to 70 centimetres in length - too big to make ideal pets.

The number of protected turtles seized in Hong Kong has grown substantially in the past three years, from 155 in 2008 to 2,099 in last year.

It is not easy to return wild animals to their original homes, Wong said. 'It is not easy because most countries do not want to be involved in this and there are cultural and language barriers too.'

Dr Gary Ades, head of fauna conservation at Kadoorie Farm, said it had taken a lot of time and work to return the animals into the wild. They will be released in an area free of poachers. 'We are going to release them in the upstream of the river, away from human activities,' he said.

Tan Kit-sun, Kadoorie's senior conservation officer, said it was important to transfer the turtles before they grew bigger, as larger turtles become aggressive and fight each other. The turtles stand a very high chance of surviving to maturity, he said, although it would be impossible to monitor them after they are released into the wild. The biggest threat they will face, other than poachers, is natural predators such as crocodiles.

50%

The percentage decline in the wild population of freshwater pig-nosed turtles in the last 20 years, according to a study this year